1. Field of the invention
The present invention relates to a method for manufacturing an x-ray detector, and more particularly to a method for manufacturing an x-ray detector that can reduce the number of steps in a process for manufacturing it.
2. Description of the Prior Art
As generally known in the art, a film printing type x-ray photographing method is widely utilized for medical purposes. However, because printing can only be started after film is photographed, the results can only be recognized after a certain passage of time. Further, other problems exist such as safekeeping and preservation of the film after it is photographed.
As a result, conventionally, digital x-ray detectors (DXD) are studied and developed utilizing thin film transistor (TFT) arrays to overcome the above-noted problems. In this conventional x-ray detector, TFT is used as a detector.
However, the required conditions for a detector employing TFT are different from those required for an LCD employing TFT.
Specifically, the response speed is important for the conventional LCD TFT. However, signals should be transmitted as soon as x-ray detector TFT has been electrically charged, and signals are instantly transmitted to a picture after they receive x-ray signals for a comparatively long time. As a result, low off current (IOFF) properties below 0.1 pA and low line resistance are required by necessity, so that leakage currents are not produced in the pixels of the TFT.
Furthermore, an etch stopper (E/S) TFT structure is more adaptable for low off current (IOFF) properties than a back channel etch (BCE) TFT structure. Also, it is required to construct storage capacitance for a second storage electrode which is an electric charge collecting electrode (CCE) and is opposite to a first storage electrode.
As shown in FIG. 1, in the conventional x-ray detector that satisfies these requirements, gate insulating film 104a is formed on a substrate 100 upon which a gate 101, a gate pad 102 and a data pad 103 have been formed. Also, an etch stopper 108 is positioned over a channel layer 106 on the gate insulating film 104a, and an ohmic contact layer 110 and source/drain 114a, 114b are positioned over the etch stopper 108 to constitute a thin film transistor (TFT).
Additionally, a protective film 118 is formed over the thin film transistor (TFT), and a second storage electrode/electrical charge collecting electrode 122 is positioned over the protective film 118. The second storage electrode 122 is opposite to a first storage electrode 112, and a common electrode 116 is formed on the first storage electrode 112. The second storage electrode 122 contacts a portion of the source/drain 114a, 114b by way of a contact hole 120.
This x-ray detector radiates x-rays from x-ray sources to a predetermined objects such as human body and forms corresponding images from the emitted signals in a TFT detector. In particular, as the detected signals of the TFT detector are digitalized, they are more favorable for long distance transmission.
However, there are certain problems, as explained below, in x-ray detectors in accordance with the above-noted conventional art.
It is required to form an etch stopper for the conventional x-ray detector having low off current properties, as noted above, and is required to form a second storage electrode/electrical charge collecting electrode in order to form a storage capacitance.
As a result, several steps are required to manufacture an x-ray detector in accordance with the conventional art. That is, masking for forming a gate, masking for forming an etch stopper, masking for forming an active layer, masking for forming a first storage electrode, masking for forming contact holes, masking for forming source/drain, masking for forming a protective layer, and masking for forming a second storage electrode, etc., is required.
As stated above, because eight masking steps are required to manufacture the conventional x-ray detector, the process for manufacturing an x-ray detector is complicated, the possibility of producing inferior products is high, and manufacturing costs of the x-ray detector increase.
Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a method for manufacturing an x-ray detector, which can reduce the number of masking processes to result in the reduction of production costs, and enhance productivity by minimizing the possibility of occurrence of inferior products.
In order to accomplish this object, there is provided a method for manufacturing an x-ray detector, the method comprises the steps of: preparing an insulating substrate; forming a gate and a pad on the insulating substrate; forming a gate insulating film, an amorphous silicon layer and an etch stopper over the insulating substrate, inclusive of the gate and the pad; simultaneously forming a channel layer, an ohmic contact layer and a source/drain over the gate insulating film, inclusive of the etch stopper, and a common electrode over a proper portion of the gate insulating film; forming a first storage electrode over the gate insulating film, inclusive of the common electrode; forming a protective layer over the entire structure of the insulating substrate on which the source/drain and the first storage electrode have been formed, and subsequently forming a contact hole and via holes over a proper portion of the protective layer; and forming a second storage electrode over the protective layer.